Bumetanide attenuates acute lung injury by suppressing macrophage activation

Bumetanide is a potent loop diuretic that acts as an inhibitor of sodium-potassium-chloride cotransporter 2 (NKCC2) and its isoform NKCC1. Although the expression of NKCC2 is limited to the kidney, NKCC1 is widely expressed in various cells, where it participates in a variety of physiological functions including ion transport, alveolar fluid secretion, and cell volume regulation. We investigated the role of NKCC1 in modulation of host immunity. Lipopolysaccharide (LPS) stimulated the expression and phosphorylation of NKCC1 in RAW264.7 cells in vitro and activated these cells to produce inflammatory cytokines. Enlarging the cell volume in a low-osmotic microenvironment amplified the LPS-induced inflammatory responses and phagocytosis activity of RAW264.7 cells. Pretreatment with the NKCC1 inhibitor bumetanide attenuated LPS-induced activation of inflammatory cells and cell volume-related function. Mice treated with an intratracheal bumetanide spray showed greater resistance to LPS-induced tissue inflammation and acute lung injury in vivo. Our studies suggest that NKCC1 plays a unique role as an amplifier of LPS-induced macrophage functions and that NKCC1 might be a novel target for treating sepsis-related acute respiratory distress syndrome.